A head-mounted display (HMD) refers to various image display devices such as glasses that are worn on a user's head to allow the user to view images (contents). Various wearable computers have been developed depending on the trend of weight reduction and size reduction of digital devices, and the HMD is also widely used. The HMD may be combined with an augmented reality technology, an N-screen technology, etc., beyond a simple display function, to provide various conveniences to the user.
Recently, with the increase in the use of the HMD, methods of performing various functions according to a posture of the HMD are being actively developed. Here, the posture of the HMD is a concept including a placed state of the HMD (a worn state on the user's head), a tilted degree of the HMD, a direction that the HMD faces, a position of the HMD, a rotation of the HMD, a movement of the HMD, and the like.
In the related art, an inclination or a movement of the HMD has been detected by using sensors mounted on the HMD or the like, and the posture of the HMD has been determined based on the detected result. However, in such a method, it is difficult to detect the movement of the HMD when the HMD moves in a horizontal direction without being tilted (for example, when the HMD moves in parallel to front, rear, right and left without being tilted).
Accordingly, when a taken (captured) image of a specific subject is changed according to the movement (motion) of the main body, a method of analyzing the image change of the specific subject included in the taken image to recognize the movement of the main body may be implemented. This method may enable a determination of even a movement of the HMD in a horizontal direction without being tilted as well as a tilted movement of the HMD. Accordingly, various functions can be more effectively controlled according to the movement of the main body.
However, this method fails to precisely recognize the movement of the main body when the specific subject is not located within a specific viewing angle range (or a specific range of field of view) any more due to the movement of the main body, which results from particularity that a camera forming the taken image is capable of capturing only the specific viewing angle range.